The spectrum will increasingly become a scarce resource for point-to-point deployment connections, and many frequencies are currently saturated in dense urban areas. The very strict ETSI class 4 standard makes it possible to deploy more links in a given spectrum and to increase the ability to transport data with less interference.
In order to create compact antenna systems, dual-reflector antennas are used, particularly so-called “Cassegrain” antennas. The dual reflector includes a concave main reflector, most commonly a parabola or portion of a parabola, and a convex sub-reflector, much smaller in diameter, placed in the vicinity of the focus of the parabola on the same revolution axis as the main reflector. A feed source is located along the antenna's axis of symmetry, facing the sub-reflector. These antennas are called “deep-dish” antennas, with a low f/D ratio, less than or equal to 0.25, where f is the focal distance of the main reflector (distance between the apex of the reflector and its focus) and D is the diameter of the main reflector.
In order to meet the criteria of the ETSI class 4 standard, an antenna requires a high radio frequency. The main challenge is to obtain an antenna pattern with a very low level of secondary lobes, in particular for an antenna with a D/λ ratio (D: Diameter of the main reflector and λ: wavelength of the central frequency in the antenna's working frequency band) of less than 30. In that frequency range, the masking effect of the sub-reflector increases the secondary lobes.
These antennas exhibit spillover losses that are high and reduce the front-to-back ratio of the antenna. These spillover losses lead to the environment being polluted by RF waves. The spillover losses must therefore be limited to very low levels, as required by the ETSI class 4 standard.